The impact of nucleoside base modification in mRNA vaccine is influenced by the chemistry of its lipid nanoparticle delivery system.

The use of modified nucleosides is an important approach to mitigate the intrinsic immunostimulatory activity of exogenous mRNA and to increase its translation for mRNA therapeutic applications. However, for vaccine applications, the intrinsic immunostimulatory nature of unmodified mRNA could help induce productive immunity. Additionally, the ionizable lipid nanoparticles (LNPs) used to deliver mRNA vaccines can possess immunostimulatory properties that may influence the impact of nucleoside modification. Here we show that uridine replacement with N1-methylpseudouridine in an mRNA vaccine encoding influenza hemagglutinin had a significant impact on the induction of innate chemokines/cytokines and a positive impact on the induction of functional antibody titers in mice and macaques when MC3 or KC2 LNPs were used as delivery systems, while it impacted only minimally the titers obtained with L319 LNPs, indicating that the impact of nucleoside modification on mRNA vaccine efficacy varies with LNP composition. In line with previous observations, we noticed an inverse correlation between the induction of high innate IFN-α titers in the macaques and antigen-specific immune responses. Furthermore, and consistent with the species specificity of pathogen recognition receptors, we found that the effect of uridine replacement did not strictly translate from mice to non-human primates.

A novel lamprey antibody sequence to multimerize and increase the immunogenicity of recombinant viral and bacterial vaccine antigens.

Hemagglutinin, the major surface protein of influenza viruses, was recombinantly expressed in eukaryotic cells as a monomer instead of its native trimer, and was only immunogenic when administered with an adjuvant [Pion et al. 2014]. In order to multimerize this antigen to increase its immunogenicity, a cysteine-rich peptide sequence found at the extreme C-terminus of lamprey variable lymphocyte receptor (VLR)-B antibodies was fused to various recombinant hemagglutinin (rHA) proteins from A and B influenza virus strains. The rHA-Lamp fusion (rHA fused to the lamprey sequence) protein was expressed in Leishmania tarentolae and Chinese hamster ovary (CHO) cells and shown to produce several multimeric forms. The multimers produced were very stable and more immunogenic in mice than monomeric rHA. The lamprey VLR-B sequence was also used to multimerize the neuraminidase (NA) of influenza viruses expressed in CHO cells. For some viral strains, the NA was expressed as a tetramer like the native viral NA form. In addition, the lamprey VLR-B sequence was fused with two surface antigens of Shigella flexneri 2a, the invasion plasmid antigen D and a double mutated soluble form of the membrane expression of the invasion plasmid antigen H namely MxiH. The fusion proteins were expressed in Escherichia coli to produce the respective multimer protein forms. The resulting proteins had similar multimeric forms as rHA-Lamp protein and were more immunogenic in mice than the monomer forms. In conclusion, the VLR-B sequence can be used to increase the immunogenicity of recombinant viral and bacterial antigens, thus negating the need for adjuvants.

[Phages and vaccination: towards new opportunities?] / Phages et vaccination : vers de nouvelles opportunités ?

Bacteriophages, or phages, are ubiquitous microorganisms that only infect bacteria. They were briefly used, mainly in the West, in the early 20th century to treat human bacterial infections, before being replaced by antibiotics in the 1940s. In the 1970s, the phage display technology, which consists of presenting multiple copies of small polypeptides at the surface of the phage, led to consider phages as vaccine antigen producers. However, the technology potential for this use remains limited to small or truncated antigens that required the use of an adjuvant. Nowadays, phages are gaining a growing interest as vaccine antigen delivery vehicles. Evidence of the phage intrinsic adjuvant properties, which can be enhanced by targeting the particles to various eucaryotic cells, combined with a demonstrated inocuity in human and at low production cost make it possible to envisage in a near future the use of virus-based vaccines-like phagic particles (i.e. virus-like particles). This review describes, in a non-exhaustive way, some of the most promising technological approaches. In addition, there is a growing body of evidence from the literature showing that phages play a major role in the equilibrium of the human intestinal microbiota and protection against mucosal infection, opening new opportunities for vaccine research, targeting pathogens at the first natural host barrier protection.